Prodcution of polymer/food grade solvents from paraffin rich low value streams employing hydroprocessing

ABSTRACT

The present invention relates to the process for the preparation of Polymer/Food grade hydrocarbon solvents of naphtha range essentially free from olefins less than 20 ppm of aromatics and less than 1 ppm of sulfur from paraffinic-rich low value streams such as raffinate from the solvent extraction units in crude oil refineries employed for recovery of aromatics from reformate by hydrogenation in the presence of a nickel based catalyst.

FIELD OF THE INVENTION

The present invention relates to the process for the preparation ofPolymer/Food grade hydrocarbon solvents of naphtha range essentiallyfree from olefins less than 20 ppm of aromatics and less than 1 ppm ofsulfur from paraffinic-rich low value streams such as raffinate from thesolvent extraction units in crude oil refineries employed for recoveryof aromatics from reformate by hydrogenation in the presence of a nickelbased catalyst.

BACKGROUND OF THE INVENTION

Petroleum naphtha is a widely used solvent both in industry andlaboratories. Different grades of naphtha solvents are available forvarious applications. These solvents are normally used as

-   a) an ingredient in the finished product,-   b) solvents for extraction of vegetable oil (from oil seeds),    minerals, pharmaceuticals,-   c) solvents for reactants e.g. in polymerization reactor and-   d) solvents for cleanup and maintenance operations.

These solvents are manufactured from low boiling refinery streams likenaphtha and find their applications in agriculture, food andpharmaceuticals, petrochemicals, printing, paint and coating, chemicalindustries etc.

Though, there does not exist any universally accepted nomenclature forhydrocarbon solvents, most manufacturers group their solvents accordingto boiling point and composition. Distillation range is also one of themain criteria. Solvent grades with narrow and wide boiling ranges, alsoreferred to as “Special Boiling Point Spirits” (SBPS) are generallyfound in the boiling range of 45-160° C. White spirit is the name givento solvents in the boiling range of 150-220° C. Composition is anotherimportant parameter for characterizing the solvents. Depending upon thetype of compounds present in the solvents, they are named such asaromatic solvents, Isoparaffinic solvents. For most of the polymers andresins, solvent power is found in the following order:

-   Aromatics>Naphthenes>n-Paraffins>i-Paraffins

Aromatics are known to have maximum solubilizing power. However, fromtoxicological and performance point of view, benzene-free and very lowaromatic content solvents are required in applications e.g. Oil seedextraction, polyolefins manufacture, printing inks and adhesives.Evaporation rate, appearance, color and odor are some of the otherimportant characteristics of solvents. When the solvents consist mainlyof a single hydrocarbon, they are named after the same e.g. Hexane,Isohexane, Heptane etc.

In an extraction processes, the function of the solvent is to extractselectively some particular ingredient from a mixed product or rawmaterial e.g. vegetable oils, pharmaceuticals, cleaning & degreasingetc. For food processing and pharmaceutical applications, criteria mustbe strictly qualified with respect to present of compounds havingtoxicological properties. In chemical process, the function of thesolvent is to act as an inert reaction medium or catalyst carrier e.g.in polyolefins manufacture. In these and other process, apart frombenzene and other aromatics content, strict specifications aremaintained with respect to olefins, Sulfur also.

The product form Hydrocracking unit are very low in aromatics.Therefore, fractionation of hydrocracker naphtha into suitable boilingranges is often done to produce dearomatised solvents. But hydrocrackernaphtha is a premium product and has other preferred uses e.g. feedstockfor reforming, ethylene cracking etc. The ‘S’ content in Hydrocrackernaphtha quite often exceeds 1 ppm due to recombination of H₂S andolefins into mercaptans. This amount of sulfur is unacceptable in FoodGrade and Polymer Grade solvents. Catalytic hydrogenation of StraightRun Naphtha streams is another option. However, the sulfur present inthese streams require prior desulfurisation and the higher pressureprocess employing sulfided catalysts are uneconomical. Patents describeprocesses for hydrogenation of benzene in heterogeneous reactor eitherin liquid phase (U.S. Pat. No. 4,327,234: Hydrogenation process usingsupported nickel catalyst) or in gas phase (U.S. Pat. No. 5,771,86:Process for hydrogenating benzene in hydrocarbon oils) as well as inhomogeneous reactor (U.S. Pat. No. 5,668,293: Catalyst and a benzenehydrogenation process using said catalyst). Patents also describeproceses for benzene hydrogenation through catalytic distillation (U.S.Pat. No. 6,084,141: Hydrogenation process comprising a catalyticdistillation zone comprising a reaction zone with distribution ofhydrogen, U.S. Pat. No. 6,048,450: Process for the selective reductionto the content of benzene and light unsaturated compounds in ahydrocarbon cut). However, all these processes are meant for meetingbenzene specifications in MS where benzene is required to be reduced to1 vol % only to meet the most stringent Euro-IV standard. In addition tohydrogenation of benzene in fuels, patents describe processes forproduction of cyclohexane also through hydrogenation of Benzene (U.S.Pat. No. 5,589,600: Preparation of cyclohexene by partial hydrogenationof benzene).

Solvent extraction is another method used for the production ofdearomatised solvents. A patent (IN 168536) describes such a process ofSeparation of benzene and C5-6 non-aromatic hydrocarbons from naphthafractions by countercurrent extraction for recovery of food-graden-hexane.

However, for very low aromatics concentration in solvents, solventextraction would be prohibitively expensive. Moreover, solvent extractedparaffins have relatively lower solvent power in comparison tohydrogenated solvents, as the naphthenes from saturation partlycompensate for the solvent power of the aromatics. Moreover, solventextracted solvents may not be able to meet the specifications forBromine member (olefins).

Adsorptive dearomatisation using silica gel, alumina and activatedcarbon has not so far been attractive for large scale commercialproduction due to requirements for continuous regeneration. Acidic claysalso been used for production of solvents. But they only remove olefins,not aromatics. Two patents (IN 184574 & IN 179409) describe methods toproduce Food Grade Hexane through adsorption and clay treatment.

SUMMARY OF THE INVENTION

The present invention generally relates to a catalytic hydrogenationprocess for the preparation of polymer/food grade hydrocarbon solventsin naphtha range essentially free from olefins and having aromatics lessthan 20 ppm and sulfur less than 1 ppm nil olefins from naphtha rangepetroleum stock and more preferably from raffinate obtained from BTXextraction unit, e.g. Udex, using a Nickel based catalyst.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a catalytic hydrogenation process forthe preparation of polymer/food grade hydrocarbon solvents of naphtharange containing very low aromatics, especially benzene less than 20 ppmfrom naphtha range petroleum stock. More particularly, the presentinvention relates to a catalytic hydrogenation process for thepreparation of polymer/food grade hydrocarbon solvents of naphtha rangeessentially free of olefins, containing aromatics less than 10 ppm andcontaining sulfur less than 1 ppm from paraffinic rich solvents whichare substantially free from Sulfur, chlorides.

The present invention provides a process for preparing polymer/foodgrade hydrocarbon solvents of naphtha range containing very lowaromatics, especially bezene less than 20 ppm from naphtha rangepetroleum stock, said process comprising:

-   a. heating the naphtha range petroleum feed to a temperature in the    range of 70°-180° C.;-   b. adding stoichiometric amount of hydrogen to the naphtha range    petroleum feed at a pressure between about 5 to 30 bar;-   c. passing the mixture of feed and hydrogen through a reactor having    a nickel based catalyst, and-   d. removing any excess hydrogen to obtain polymer/food grade    hydrocarbon solvents of naphtha range containing very low aromatics.

In an embodiment of the present invention, the naphtha range petroleumfeed is preferably raffinate from the solvent extraction units employedfor recovery of aromatics from reformate. In another embodiment of thepresent invention, the raffinate feed has sulfur<50 ppm, preferably <5ppm and most preferably <1 ppm.

In yet another embodiment of the present invention, the raffinate feedhas aromatics<20% by wt and preferably <10% by wt.

In still another embodiment of the present invention, the raffinate feedhas benzene<20% by wt and preferably <10% by wt.

In a further embodiment of the present invention, the raffinate feed hasboiling point in the range of C₅ to 110° C.

In one more embodiment of the present invention, the raffinate feed hasboiling point in the range of 63°-70° C.

In one another embodiment of the present invention, the raffinate streamhas about 4 to 7% by wt benzene.

In an embodiment of the present invention, the catalyst is nickelsupported on alumina catalyst.

In another embodiment of the present invention, the nickel loading isabout 10 to 70% by wt. and preferably is about 30 to 60% by wt.

In still another embodiment of the present invention, the metal surfacearea of the nickel-alumina catalyst is about 10-20 m²/g.

In yet another embodiment of the present invention, the physical surfacearea of the nickel-alumina catalyst is about 120-200 m²/g and the porevolume of the catalyst is about 0.2-0.3.

Feed: The feed is of naphtha range having boiling range of C₅-110° C. Inparticular, the feed should have boiling point in the range of 63°-70°C. for producing Food/Polymer grade hexane. The feed should besubstantially free from Sulfur i.e. the sulfur content in the feedshould be <50 ppm), more preferably <5 ppm and most preferably <1 ppm.The amount of the aromatics in the feed should be <20% and morepreferably less than 10%. The Applicants have found that Raffinates ofBTX extraction column post reforming make excellent feed stockqualifying the necessary feed properties. In a most preferred embodimentof the present invention, Udex raffinate having a boiling point of63°-70° C. is used for the production of Food/Polymer grade Hexanesubstantially free of benzene and aromatics.

In the present invention, the feed is reacted with Hydrogen in presenceof a catalyst at a temperature range of 70-180° C. and under a pressureof 10 to 30 bars. The reaction is carried out preferably in a threephase reactor and more preferably the reaction is conducted in a tubularfixed bed reactor and most preferably, in a down flow Trickle BedReactor.

Catalyst: In the present invention, Metals of Group VIII supported oninert material are used to catalyze the hydrogenation reaction. Moreparticularly, nickel supported on alumina is a preferred catalyst.Nickel loading is from 10-70 wt % and more preferably from 30-60 wt %.The metal surface area is between 10-20 m²/g. The physical surface areaof the support material after impregnation of Nickel is between 120-200m²/g. The pore volume of the catalyst is between 0.2-0.3 cc/gm. Thecrushing strength of the catalyst is above 1 MPa. Nickel Oxide on thecatalyst is reduced to its active form Ni in the reactor at 380° C.-420°C. with Hydrogen. In another preferred embodiment, the catalyst isreduced ex-situ and then exposed to a mixture of 1-4% O₂ to give acoating of inert oxide on the active catalyst for safe handling. Afterloading in the reactor under inert nitrogen, the outer inert oxidedlayer is reduced at 160° C.-200° C. under hydrogen flow rate.

In this process Feed is heated to the reaction temperature which isbetween 70-180° C., and preferably between 80-150° C. Hydrogen is mixedwith Feed at the pressure between 5 to 30 bar and more preferablybetween 10 to 20 bar. Hydrogenation reaction takes place in the reactoron the active sites of catalyst under operating conditions as describedabove. The product coming out of the reactor is separated from unreactedHydrogen in a separator Very little hydrogen is introduced in excess tothe stoichiometric amount to the reactor. As a result, there is no needfor recycle of un-reacted Hydrogen. In one embodiment of the process, abed of sulfur guard adsorbents is placed in the reactor before catalystwhen ‘S’ level in feed is higher than 5 ppm. In another embodiment ofthe process, a bed of chloride guard adsorbents are placed in thereactor before catalyst when ‘Cl’ level in feed is higher than 1 ppm.

In another embodiment of the process, a dryer of Molecular Sieve isplaced before the reactor. When moisture in feed is higher than 1 ppm.Product from the reactor is hydrocarbon stream of same boiling range asthat of Feed and substantially free from Aromatics, more particularly,Benzene.

The invention will be further illustrated by the following examples.While the Examples are provided to illustrate the present invention,they are not intended to limit it.

EXAMPLE—1

The raffinate streams of a reformate extraction unit has the followingcomposition: Component % wt 2,3 dienethyl Butane 4.1 2 Methyl Pertane18.7 3 Methyl Pertane 15.0 N-Hexane 23.4 Methyl Cyclopertane 4.5 Benzene7.2 Methyl Hexane 13.2 N Heptane 7.4 Tolune 6.5

This was fed along with hydrogen to a tubular reactor having catalyst offollowing properties.

Catalyst Characteristics Chemical composition NiO₂/Al₂O₃ PhysicalSurface area 162 m²/gm Pore volume 0.221 cc/gm Av. Pore diameter 55 A°Bulk Crushing strength 1.96 Mpa Metal Surface Area 14.82 m²/gm Metaldispersion 5.6%

The catalyst was activated under H₂ flow at atmospheric pressure and400° C. to reduce the oxided Nickel to Ni.

The results of the runs are as following properties: Run LHV TemperaturePressure Aromatics in products No. 1 in hr¹ in ° C. Kg/cm²g BenzeneTolune 1. 4.0 100 30 50 ppm ND 2. 4.0 140 20 30 ppm ND 3. 4.0 120 15 60ppm ND 4. 2.0 100 15 72 ppm ND 5. 2.0 120 20 45 ppm NDND: Not detected

EXAMPLE—2

A heart cut was prepared from a Naphtha stream from the raffinate of aUdex unit and this was hydrotreated in a Trickle Bed Reactor.

The catalyst properties are as following:

Catalyst Characteristics Chemical composition NiO₂/Al₂O₃ Ni Content 40%Metal surface area  20 m²/gm Physical surface area 170 m²/gm Crushingstrength 1.3 Mpa

The catalyst was pre-reduced under Hydrogen and then a thin oxide layerwas formed by exposed the catalyst to a mixture of 1% O₂. After loadingthe catalyst into the reactor, it was reduced at 180° C. with Hydrogen.

The operating condition of the run are as follows Feed space velocity,hr¹. 1.3 Inlet Temperature, ° C. 95 Pressure, kg/cm²g 18 H₂ flow rate,Nm³/m³ of feed 28.5

The feed and Product composition are as follows: % wt/wt S. No.Component Feed Product 1. 2.2 Dimethyl butane 2. Cyclopentane 2,3DiMethyl butane 1.00 1.06 3. 2 Methyl pentane 9.73 10.98 4. 3 Methylpentane 21.14 25.84 5. n-Hexane 53.56 52.90 6. Trans-2-hexene- 0.35 — 7.2- Methyl penetene-2 0.49 — 8. 4-Methyl penetene-2 0.33 — 9.Cis-2-hexane 0.18 — 10. 3 Methyl pentene-2 0.50 — 11. 2.2 DiMethylpentane 0.25 — 12. Methyl cyclopentane 7.48 5.68 13. 2,4 DiMethylpentane 0.36 — 14. Benzene 4.02 ND* 15. 3,3 DiMethyl pentane 0.04 — 16.Cyclohexane 0.29 3.54 17. 2-Methyl hexane 0.13 — 18. 2.3 DiMethylpentane 0.05 — 19. 3-Methyl hexane 0.10 — 100.0 100.00ND (Not detected)*: Less than 20 ppm

1. A process for preparing polymer/food grade hydrocarbon solvents ofnaphtha range containing very low aromatics, especially bezene less than20 ppm from naphtha range petroleum stock, said process comprising: a.heating the naphtha range petroleum feed to a temperature in the rangeof 70°-180° C.; b. adding stoichiometric amount of hydrogen to thenaphtha range petroleum feed at a pressure between about 5 to 30 bar; c.passing the mixture of feed and hydrogen through a reactor having anickel based catalyst; d. removing any excess hydrogen to obtain thepolymer/food grade hydrocarbon solvents of naphtha range containing verylow aromatics.
 2. A process as claimed in claim 1, wherein the naphtharange petroleum feed is preferably raffinate from the solvent extractionunits employed for recovery of aromatics from reformate.
 3. A process asclaimed in claim 1, wherein the raffinate feed has sulfur<50 ppm,preferably <5 ppm and most preferably <1 ppm.
 4. A process as claimed inclaim 1, wherein the raffinate feed has aromatics<20% by wt andpreferably <10% by wt.
 5. A process as claimed in claim 1, wherein theraffinate feed has benzene<20% by wt and preferably <10% by wt.
 6. Aprocess as claimed in claim 1, wherein the raffinate feed has boilingpoint in the range of C₅ to 110° C.
 7. A process as claimed in claim 1,wherein the raffinate feed has boiling point in the range of 63°-70° C.8. A process as claimed in claim 1, wherein the raffinate stream hasabout 4-7% by wt benzene.
 9. A process as claimed in claim 1, whereinthe catalyst is nickel supported on alumina catalyst.
 10. A process asclaimed in claim 1, wherein the nickel loading is about 10 to 70% by wt.and preferably is about 30 to 60% by wt.
 11. A process as claimed inclaim 1, wherein the metal surface area of the nickel-alumina catalystis about 10-20 m²/g.
 12. A process as claimed in claim 1, wherein thephysical surface area of the nickel-alumina catalyst is about 120-200m²/g and the pore volume of the catalyst is about 0.2-0.3.
 13. A processfor producing polymer/food grade solvents of naphtha range from paraffinrich hydrocarbon streams through hydroprocessing.
 14. A processaccording to claim 1 where in the product solvent contains nil olefins,Sulfur less than 1 ppm and aromatics, especially, Benzene less than 20ppm.
 15. A process according to claim 1 where in the Feed is low valueraffinate from BTX extraction column e.g. Udex unit.
 16. A processaccording to claim 1 where in the feed has maximum 20 wt % aromatics and10 wt % Benzene.
 17. A process according to claim 1 where in process iscarried out under hydrogen environment preferably at 80-150° C., and 10to 20 bar.
 18. A process according to claim 1 where in Metals of Group.VIII supported on Inert material, preferably Ni (30-60 wt %) supportedon alumina are used.
 19. A process according to claim 9 where in OxidedNi catalyst is pre-reduced before loading into the reactor.
 20. Aprocess for preparing polymer/food grade hydrocarbon solvents of naphtharange containing very low aromatics such as herein described withreference to the accompanying examples.